1. Field of the Invention
The present invention relates generally to the fields of oilfield exploration, production, and testing, and more specifically to the methods and apparatus for perforation and fracturing formations using high temperature stable explosives.
2. Background
Explosives are used in numerous downhole applications. An essential consideration in selecting explosives for use in downhole applications, such as perforating operations, is that the explosives should have a certain range of time and temperature, in which the explosives are thermally stable. That is, a given explosive will be stable at a temperature for a certain duration without appreciable decomposition or loss of performance. Typically, the higher the temperature, the shorter the duration will be, and vice versa. If the explosives are subjected to conditions beyond their stable temperature-time ranges, the explosives may start to decompose, burn, or auto-detonate. Decomposition of the explosives generally reduces their effectiveness and may cause a failure, such as a misfire (a failure to detonate).
Failures of explosives could be costly and dangerous. For example, in perforating applications, when a perforating gun string is lowered to a desired depth but for some reason cannot be activated, a mis-run has occurred. The mis-run requires that the perforating gun string be pulled out of the wellbore and replaced with a new gun string. Such replacement is both time consuming and expensive. Furthermore, retrieving a mis-fired gun from a wellbore can be dangerous.
Due to the time-temperature range considerations, use of explosive devices in downhole applications may be impractical or impossible in some situations. In many operations, where explosive actuation was desired (i.e., a device using a frangible member), alternative actuating means were selected because it may be dangerous to use the explosives in the high temperature environment. In order to use explosive devices in downhole operations, it is desirable that the temperature-time ranges of the explosives be increased, i.e., the operating time for the explosives be increased for a given temperature.
U.S. Patent Application Publication No. 2002/0129940 discloses several explosive compositions adapted for use in downhole applications where high temperature explosives are required. These high temperature explosives may be exposed to elevated temperatures for extended periods of time. Examples of these explosives include nonanitroterphenyl (NONA), octanitroterphenyl (ONT), pentanitrobenzophenone (PENCO), tetranitronaphthalene (TNN), tripicryltriazine (TPT), tetranitrobenzotriazolo [1,2-a]benzotriazole (T-Tacot), picrylaminotriazole (PATO), dinitropicrylbenzotriazole (BTX), dodecanitroquaterphenyl (DODECA), tripicrylmelamine (TPM), axobishexanitrobiphenyl (ABH), tetranitrobenzotriazolo[2,1-a]benzotriazole (Z-Tacot), potassium salt of hexanitrodiphenylamine (KHND), tripicrylbenzene (TPB), dipicramide (DIPAM), hexanitroazobenzene (HNAB), bis-hexanitroazobenzene (bis-HNAB), hexanitrobiphenyl (HNBP), dipicrylbenzobiatriazoledione (DPBT), dipicrylpyromellitude (DPPM), hexanitrodiphenylsulfone (HNDS), and bis[picrylazo]dinitropyridine (PADP-I), sodium tetranitrocarbozole (NaTNC), hexanitrobibenzyl (HNBIB), tetranitro carbazole (TNC), 3,6 diamino 1,2,4,5 tetrazene (DAT), 2,6-diamino-3,5-dinitropyridino-1-oxide (DADNPO), octanitromacro cycle (ONM), 4,6 dinitrobenzofuroxan (ADNBF), 2,5-dipcryl -1,3,4-oxadiazole (DPO) and m-picrylpicramide (PIPA).
Though these high temperature stable explosives are useful for downhole applications, such as in perforating applications, tubing and casing cutters, explosive-actuated sleeves, sonic or seismic fracing devices, explosively setting devices, explosively opening production valves, explosive actuated sliding sleeves (valves or shuttles), breakable or frangible elements, tubing release devices, actuating devices, and propellant assemblies. There is still a need for explosives with improved thermal stability for downhole use.